Continuously rotating grating rapid-scan spectrophotometer

Claim 2

A monochromator comprising: a source of polychromatic radiation (10) and means (12,14) to direct the radiation to an optical grating (18), an optical grating (18) located in the path of said radiation, said grating being mounted to a shaft (28) for rotation, means (26,38) for continuously rotating the shaft and grating at an approximately constant uninterrupted angular velocity, a shaft encoder assembly (42,44) mounted on and adjacent said shaft (28) to deliver information represen­ting specific angular positions of the shaft (28), and an electronic logic circuit (48,50) delivering pulses in response to information received from said shaft encoder assembly (42,44) whenever a specific wavelength is to appear at the exit slit (20).

Claim 3

The monochromator as claimed in claim 1 wherein the grating (18) is rotated about its optical axis.

Claim 4

The monochromator as claimed in claim 1 wherein said shaft (28) and said grating (18) are mounted on a turntable (26) of relatively high mass for rotation therewith.

Claim 5

The monochromator as claimed in claim 1 wherein said logic circuit (48,50) defines the position at which said specific wavelength appears at the exit slit (20) by sensing the angular velocity and acceleration of the grating (18).

Claim 6

The monochromator as claimed in claim 4 wherein said shaft encoder assembly (42,44) produces index pulses and said logic circuit (48,50) delivers a pulse whenever a specific wavelength appears at the exit slit (20) by interpolating the time interval between two successive index pulses delivered by the shaft encoder assembly (42,44).

Claim 7

A monochromator as claimed in claim 1 wherein the means of rotating the grating (18) include a motor (38) and a motor control to set the motor speed.

Claim 8

The monochromator as claimed in any of claims 1 to 6 inclusive additionally comprising a filter wheel (16) synchronized with the rotation of the grating (18).

Claim 9

A spectrophotometer incorporating the monochromator claimed in any of claims 1 to 6 additionally comprising a sample cell (22) through which the monochromatic radiation delivered by the monochromator passes and a detector (24) intercepting the radiation creating an electrical signal representing the intensity of the radiation passing through said sample cell (22).

Claim 10

The spectrophotometer as claimed in claim 8 addi­tionally comprising a filter wheel (16) synchronized with the rotation of the grating (18).

Claim 11

The spectrophotometer as claimed in claim 8 inclu­ding a non-reflecting back surface of the grating, and additionally including continuous dark current compen­sation obtained by measuring the electrical dark current signal produced by the detector when the non-reflecting back surface of the grating intercepts the radiation and correcting the signal values representing spectral data with the dark current signal value.

Claim 12

A spectrophotometer comprising: a source of polychromatic radiation (10) and means (12,14) to direct the radiation to an optical grating, an optical grating (18) located in the path of said radiation, a rotatable shaft (28) attached to said grating, means (26,38) for continuously rotating the shaft and grating at an approximately constant uninterrupted angular velocity, an angular shaft encoder assembly (42,44) mounted on and adjacent said shaft to deliver information representing specific angular positions of the shaft, an electronic logic circuit (48,50) delivering pulses in response to information received from said shaft encoder assembly, a sample cell (22) located in the path of monochromatic radiation from the rotating grating and a detector (24) positioned to intercept the radiation existing the sample cell, said detector creating an electrical signal repre­senting the intensity of the radiation passing through said sample cell, and a sampling circuit (52) receiving said pulses from the electronic logic circuit and continuously receiving the elec­trical signal from the detector to thereby sample the continuous electrical signal in response to pulses received and produce a spectrum of radiation intensity values relative to specific wavelengths.

Claim 13

A spectrophotometer comprising: a source of polychromatic radiation (10) and means (12,14) to direct the radiation to an optical grating, an optical grating (18) located in the path of said radiation, a rotatable shaft (28) attached to said grating, means (26,38) for continuously rotating the shaft and grating at an approximately constant uninterrupted angular velocity, an angular shaft encoder assembly (42,44) mounted on and adjacent said shaft to deliver information representing specific angular positions of the shaft, an electronic logic circuit (48,50) delivering pulses in response to information received from said shaft encoder assembly, a sample cell (22) located in the path of monochromatic radiation from the rotating grating and a detector (24) positioned to intercept the radiation existing the sample cell, said detector creating an electrical signal repre­senting the intensity of the radiation passing through said sample cell, and a sampling circuit (52) receiving said pulses from the electronic logic circuit and continuously receiving the elec­trical signal from the detector to thereby sample the continuous electrical signal in response to pulses received and produce a spectrum of radiation intensity values relative to specific wavelengths.

Claim 14

The spectrophotometer as claimed in claim 11 wherein said sampled radiation intensity values are presented in digitized form.

Claim 15

A spectrophotometer as claimed in claim 11 incorporating a trigger circuit initiating the sampling cycle before the first wavelength of interest intercepts the detector.

Claim 16

The spectrophotometer as claimed in claim 11 wherein said angular shaft encoder assembly delivers an index pulse (46) for each revolution and said trigger circuit starts the sampling cycle in response to said index pulse.

Claim 17

The spectrophotometer as claimed in claim 14 wherein the detector senses the zero order spectrum (polychromatic radiation relfected by the grating) and produces a signal by which the angular position of the shaft is verified by the relation of this signal to the index pulse (46).

Claim 18

The spectrophotometer as claimed in claim 12 including associated circuitry comprising a scratch-pad memory buffer (58) receiving digitized data from said sampling circuit in real time and adapted to transmit said data to subsequent processing units.

Claim 19

The spectrophotometer as claimed in claim 16 wherein the data from said scratch-pad memory buffer (58) are trans­mitted to vacate the buffer for a burst of fresh data from from the following scanning cycle during the next revolution of the grating.

Claim 20

The spectrophotometer as claimed in claim 16 including subsequent processing units (62) comprising direct processing means, permanent storage (64) and means for retrieving infor­mation from said permanent storage for processing in conjunction with said direct processing means.

Claim 21

The spectrophotometer as claimed in any of claims 11, 15, 16, 17 or 18 including a non-reflecting back surface of the grating, and additionally including continuous dark current compensation obtained by measuring the electrical dark current signal produced by the detector when the non-reflecting back surface of the grating intercepts the radiation and correcting the signal values representing spectral data with the dark current signal value.

Claim 22

A spectrophotometer comprising: a source of polychromatic radiation (10) and means (12,14) to direct said radiation to an optical grating (18), an optical grating (18) located in the path of said radiation, said grating being mounted for rotation about the optical axis of the grating at an approximately constant uninterrpupted angular velocity, a sample cell (22) through which the diffracted radiation passes, detector means (24) to intercept said radiation and deliver a continuous electrical signal representing the intensity of radiation impinging on said detector after passing through said sample cell, means (42,44) for sensing the actual angular position of said grating, means (48,50) for producing signals representing the selected wavelengths at which the spectral data are to be measured, and means for sampling (52) the continuous electrical signal produced by said detector in response to said signals representing said selected wavelengths.

Claim 23

A spectrophotometer comprising: a source of polychromatic radiation (10) and means (12,14) to direct said radiation to an optical grating (18), an optical grating (18) located in the path of said radiation, said grating being mounted for rotation about the optical axis of the grating at an approximately constant uninterrpupted angular velocity, a sample cell (22) through which the diffracted radiation passes, detector means (24) to intercept said radiation and deliver a continuous electrical signal representing the intensity of radiation impinging on said detector after passing through said sample cell, means (42,44) for sensing the actual angular position of said grating, means (48,50) for producing signals representing the selected wavelengths at which the spectral data are to be measured, and means for sampling (52) the continuous electrical signal produced by said detector in response to said signals representing said selected wavelengths.

Claim 24

The spectrophotometer as claimed in claim 20 wherein the means for sensing the actual position of the grating includes a pulse producing shaft encoder assembly (42,44) mounted on and adjacent the shaft (28) about which said grating (18) is rotated.

Claim 25

The spectrophotometer as claimed in claim 20 wherein said grating and shaft are affixed to a relatively heavy turntable (26).

Claim 26

The spectrophotometer as claimed in claim 21 wherein said means for producing said selected wavelengths include an electronic logic circuit (48,50) producing signal pulses in response to pulses produced by the shaft encoder assembly, said electronic logic circuit sensing the actual angular rotational velocity and acceleration of the grating and interpolating to produce the signal pulses representing said selected wavelengths between two successive index pulses produced by the angular shaft encoder assembly.

Claim 27

The spectrophotometer as claimed in claims 21, 22 or 23 wherein the shaft encoder assembly produces an index pulse (46) for each revolution and the detector senses the zero order spectrum (polychromatic radiation reflected by the grating) impinging on the detector and produces a zero order signal, the relative angular position of the shaft, grating and detector being verified by the relation between said index pulse and said zero order signal to thereby continuously calibrate the shaft and grating to the detec­tor.

Claim 28

The spectrophotometer as claimed in claim 20 wherein the grating is rotated by means of a motor (38) and motor control to set motor speed.

Claim 29

The spectrophotometer as claimed in claim 20 addi­tionally comprising an optical filter wheel (56) rotated in synchronization with the grating.

Claim 30

The spectrophotometer as claimed in claims 20 or 23 including a non-reflecting back surface of the grating, and additionally including continuous dark current compensation obtained by measuring the electrical dark current signal produced by the detector when the non-reflecting back surface of the grating intercepts the radiation and correcting the signal values representing spectral data with the dark current signal value.

Claim 31

A monochromator comprising: a source of polychromatic radiation (10) an angularly movable optical grating (18), means (12) to direct light from the source (10) to the grating (18), and detector means (24) for detecting the intensity of substantially monochromatic radiation from the grating characterised by means for continuously rotating the grating at a substantially constant angular velocity, encoder means (42, 44) to provide electrical signals representative of the angular position of the grating, and electrical logic circuit means (48, 50) responsive to said electrical signals to provide control signals representative of the frequency of light detected by the detector means (24) as the grating rotates.

Claim 32

A monochromator comprising: a source of polychromatic radiation (10) an angularly movable optical grating (18), means (12) to direct light from the source (10) to the grating (18), and detector means (24) for detecting the intensity of substantially monochromatic radiation from the grating characterised by means for continuously rotating the grating at a substantially constant angular velocity, encoder means (42, 44) to provide electrical signals representative of the angular position of the grating, and electrical logic circuit means (48, 50) responsive to said electrical signals to provide control signals representative of the frequency of light detected by the detector means (24) as the grating rotates.